Vacuum tube and method of making same



Sept. 1, 1931. B. LOEWE 1,821,351

VACUUM TUBE AND METHOD OF MAKING SAME Filed March 2, 1927 lba INVENTO'RBERNHARD LOEWE BY 1a;

ATTORNEY 45 leads.

Patented Sept. 1, 1931 .UNlTED STATES PATENT OFFICE BERNHABD LOEWE, OFBERLIN-FRIEDENAU, GERMMY, ASSTGNOR TO RADIO CORPO- RATION OF AMERICA, ACORPORATION OF DELAWARE VACUUM TUBE AND METHOD OF MAKING SAMEApplication filed March 2, 1927, Serial No.

or pipe. After the process of exhaustion has been terminated, thepumping tube is withdrawn or sealed off, and this results in the wellknown tip. The avoidance of such tips is of technical importance andpractical value,

for these tips are often the cause of damage to the bulbs or tubes.

Processes have previously been disclosed to the end of making, forinstance, glowlamps and radio tubes without tips. In these processes,the tip that is sealed off is located at another place, ordinarily in'the base, in which case the tip is covered by the base and' thusprotected from damage.

of manufacturing tipless vacuum vessels from glass, quartz, or the likein such a way that no sealing tip is produced.

Therefore, it is an object of this invention 5 to provide asubstantially tipless tube.

which Figure 1 shows a resistance enclosed within a vacuum tube madeaccording to my invention, i

Figure 2 shows the tube during manufacture, and

Figure 3 shows a tube during manufacture wherein a slightly modifiedmethod of making same is utilized: P

The method will be explained by the aid of 49 the problem of makingavacuum vessel of the kind illustrated, for instance, in Figure 1.

Referring to the drawings, 1 is the glass bulb, 2 and 3 are supply leadsof any desired sort, and 4t and 5 are the seals containing said It isimmaterial in this connection what parts are located inside the vacuousves, sel, and whether the electrodes 2 and3 are located at differentends ofthe tube or bulb, or whether they are brought in at one end, or

50 whether a plurality of electrodes are sealed Now, the, 20 methodhereinafter to be described allows 171,937, and in Germany March 15,1926.

in. Merely for the sake of affording a better understanding, theassumption will be made that electrodes 2 and 3 are fused or welded intoa glass rod 6 which, for instance, may bear a resistance coat or film sothat the assembly forms what is known as a vacuum resistor of the kindused, for example, in wireless telcgraphy work. However, instead of theresistance body, also fine wires for makingvacuum-type lightningarresters may be stretched out between the electrodes, or else afilament for making rod-shaped glowlamps. As shown in the drawings, thevac-- uum vessel in Figure 1 "has no sealed-oil point at all, and thesame can be exhausted on a pump without having a sealing tip produced. 1a

The method and process will be further explained by reference to Figures2 and 3. First the glass rod-6 which carries the two electrodes 2 and 3is inserted inside the bulb, the latter having a constricted portion 5(Figure 2), at the place where the second seal is going to be. The glasshas another constricted portion 7, and is fitted to a vacuum pump atpoint 8. After the vacuum has been produced, sealing off is produced atpoint 7. After the body has been withdrawn,

it is allowed to run together at 5 by fusion so that'it comes to lieclosely around the wire 3. As soon as the seal has been made the glassis cut through or is squeezedofi", and this can be accomplished in asafe manner since the constriction at point 5 is already tightly sealedaround the electrode 3. The

cutting edges which result are thereupon molten down by a flame so thata blunt end 5 is produced.

- The method can be modified as illustrated in Figure 3. In this casethe glass bulb-previously welded onto the electrode 2 at one end isprovided only with one additional constriction, namely, at 5'. The glassbulb is again connected with the pump at 8;

vacuum space is obtained, the upper glass part 9 remains still inconnection with the lower glass part 10. After the seal at point hasbeen established by welding, air is admitted into the lower part 10 sothat the whole body can be taken off from the pump at 8. Again as inFigure 1, blowing ofi' or cutting off of the lower glass piece takes Dplace at the closure, and the edges are molten down. The final result,as in Figure 2, is a tipless vacuum body of the shape shown in Figure 1.

Mechanical severing can be effected either by cutting with the glassknife or by blasting or fusing ofl. What is essential is that beforethis is done, at a point turned towards the vacuous space, a hermeticalseal of the supply electrode or electrodes by allowing the glass tocollapse is produced. If desired and necessary for mechanical reasons,subsequent welding and Wrapping with a glass bead may be effected.

Having thus described my invention, I claim:

The method of manufacturing vacuum tubes, which comprises forming a tubewith three constrictions, sealing at least one of the electrodes to oneconstriction by closing the said constriction about the electrode,exhausting the tube'through the second and third constrictions, sealingthe tube between the second and third constrictions, and cutting ofi thetube between the second and third constrictions.

BERNHARD LoEWE.

